The present invention relates to a process for the preparation of a molecular sieve adsorbent for selectively adsorbing nitrogen and argon from a gaseous mixture with oxygen.
Adsorption processes for the separation of oxygen and nitrogen from air are being increasingly used for commercial purposes for the last three decades. Oxygen requirements in sewage treatment, fermentation, cutting and welding, fish breeding, electric furnaces, pulp bleaching, glass blowing, medical purposes and in the steel industries particularly when the required oxygen purity is 90 to 95% is being largely met by adsorption based pressure swing or vacuum swing processes. It is estimated that at present, 4-5% of the world""s oxygen demand is met by adsorptive separation of air. However, the maximum attainable purity by adsorption processes is around 95% with separation of 0.934 mole percent argon present in the air being a limiting factor to achieve 100% oxygen purity. Furthermore, the adsorption-based production of oxygen from air is economically not competitive to cryogenic fractionation of air for production levels more than 100 tonne oxygen per day. Of the total cost of the oxygen production by adsorption processes, it is estimated that capital cost of equipment and power consumption are the two major factors influencing the overall cost with their share being 50% and 40% respectively. Along with the factors like process and system design, the adsorbent is the key component, which can bring down the cost of oxygen production by adsorption. The adsorbent selectivity and capacity are important parameters for determining the size of the adsorption vessels, compressors or vacuum pumps. It is desirable to have an adsorbent, which shows a high adsorption capacity as well as selectivity for nitrogen compared to oxygen. The improvement in these properties of the adsorbent directly results in lowering the adsorbent inventory of a system and hence the size and power consumption of the air compressor or vacuum pump. Furthermore, adsorbent having a high. nitrogen capacity and selectivity can also be used to produce reasonably pure nitrogen along with oxygen by evacuating nitrogen adsorbed on the adsorbent. Furthermore, adsorbents having both nitrogen and argon selectivity over oxygen can be used for producing high purity ( greater than 96%) oxygen from air.
It is, therefore, highly desirable, for an adsorbent to have good adsorption capacity and adsorption selectivity for a particular component sought to be separated.
Adsorption capacity of the adsorbent is defined as the amount in terms of volume or weight of the desired component adsorbed per unit volume or weight of the adsorbent. The higher the adsorbent""s capacity for the desired components the better is the adsorbent as the increased adsorption capacity of a particular adsorbent helps to reduce the amount of adsorbent required to separate a specific amount of a component from a mixture of particular concentration. Such a reduction in adsorbent quantity in a specific adsorption process brings down the cost of a separation process.
The adsorption selectivity of a component results from steric factors such as the differences in the size and shape of the adsorbate molecules; equilibrium effect, i.e. when the adsorption isotherms of components of a gas mixture differ appreciably; kinetic effect, when the components have substantially different adsorption rates.
It is generally observed that for a process to be commercially economical, the minimum acceptable adsorption selectivity for the desired component is about 3 and when the adsorption selectivity is less than 2, it is difficult to design an efficient adsorption process.
In the prior art, adsorbent which are selective for nitrogen from its mixture with oxygen and argon have been reported wherein the zeolites of type A, X and mordenite have been used after ion exchanging alkali and/or alkaline earth metal ions. However, the adsorption selectivity reported for the commercially used zeolite A based adsorbents for this purpose varies from 3 to 5 and adsorption capacity from 12-15 cc/g at 765 mmHg and 30xc2x0 C. The efforts to enhance the adsorption capacity and selectivity have been reported by increasing the number of exchangeable cations into the zeolite structure by modifying the chemical composition of the zeolite. The adsorption selectivity for nitrogen has also been substantially enhanced by exchanging the zeolite with cations like lithium and/or calcium in some zeolite types.
Zeolite A having a specific amount of calcium has been commercially used for oxygen production from air by selectively adsorbing nitrogen. However, presently used adsorbent has the following limitations:
Low adsorption capacity compared to other commercially used adsorbents.
Low adsorption selectivity.
It gives oxygen with only 95% maximum purity.
Sensitivity to moisture.
It needs multiple exchange with calcium salt.
The activation of the adsorbent requires much care, in order to prevent the hydroxylation.
R. V. Jasra et al. reviewed the recent status of pressure swing adsorption as a process for separating multi component gas mixture in xe2x80x9cSeparation of gases by pressure swing adsorptionxe2x80x9d; Separation Science and Technology, 26(7), pp. 885-930, 1991, The application of a new generation of adsorbents were described in detail. In xe2x80x9cAdsorption of a Nitrogen-Oxygen mixture in NaCaA zeolites by elution Chromatographyxe2x80x9d, Ind. Eng. Chem. Res. 1993, 32, 548-552, N. V. Choudary et al. describes the influence of calcium content on adsorption of nitrogen and oxygen is studied on various NaCaA zeolite samples. N. V. Choudary et al. describes the adsorption and desorption of nitrogen, oxygen and argon in mordenite type zeolite having different Si/Al ratios in xe2x80x98Sorption of nitrogen, oxygen and argon in mordenite type zeolitesxe2x80x99, Indian Journal of Chemistry Vol. 38A January 1999, pp.34-39. The heat of adsorption of nitrogen and argon in mordenite, NaA and NaX were compared to revels the sorbate interactions with extra-frame work sodium ions as well as lattice oxygen atoms.
Reference may be made to J. J. Collins et al in U.S. Pat. No. 3,973,931(1976) entitled xe2x80x9cAir separation by adsorptionxe2x80x9d, wherein an adiabatic pressure swing process for air separation by selective adsorption in atleast two zeolitic molecular sieve beds in which air is introduced at below 90xc2x0 F., the coldest gas temperature in the inlet end is 35xc2x0 F., delta T atleast 15xc2x0 F., the inlet end is heated to maintain the gas at maximum of at least 20xc2x0 F. warner than without heating, but below 175xc2x0 F. The main drawback is it require heating and temperature control in the air separation process.
C. G. Coe et al. in U.S. Pat. No. 4,481,018 (1984) entitled xe2x80x9cPolyvalent ion exchanged adsorbent for air separationxe2x80x9d, describes the use of a thermally activated polyvalent ion exchanged faujasite-containing compositions with selectivity 3.4 to 6.7 at 30xc2x0 C. for the separation of air into oxygen and nitrogen. The drawbacks are the thermal activation process requires very slow heating to prevent hydroxylation and the selectivity of the adsorbent is only 3.4 to 6.7 at 30xc2x0 C.
S. Sircar et al in U.S. Pat. No. 4,557,736 (1985) entitled xe2x80x9cBinary ion exchanged type X zeolite adsorbentxe2x80x9d, describes the use of an adsorbent comprises a binary ion exchanged type X zeolite, in which 5%-40% of the available ion sites are occupied by calcium and 60%-95% of the available ion sites are occupied by strontium is used for the adsorption of nitrogen from an air stream at superambient pressure to produce an oxygen rich product streem. The main drawback is the preparation of the adsorbent requires multistage cation exchange process.
S. Sircar in U.S. Pat. No. 4,756,723 (1988) entitled xe2x80x9cPreparation of high purity oxygenxe2x80x9d, describes the use of a single stage pressure swing adsorption method for the production of approximately 95% pure oxygen. The main drawback is the maximum attainable oxygen purity is only 95%.
C. C. Chao in U.S. Pat. No. 4,859,217 entitled (1989) xe2x80x9cProcess for separating nitrogen from mixtures, thereof with less polar substancesxe2x80x9d, wherein highly lithium exchanged low silica form of zeolite X containing more than ninety percent lithium cations are used for the selective adsorption of nitrogen from less polar gases. These adsorbents were prepared by lithium exchanging with 4-12 fold excess LiCl3 solution. The main drawbacks are the adsorbents are highly moisture sensitive and the lithium exchange requires 4-12 fold excess LiCl3 solution.
C. G. Coe et al. in U.S. Pat. No. 4,943,304 (1990) entitled xe2x80x9cProcess for the purification of bulk gases by using chabazite adsorbentsxe2x80x9d, which provides a process for the selective adsorption of one or more minor constituents from a bulk gas stream using a chabazite. The main drawback is the known methods for preparing commercially useful synthetic chabazites are not practical since they suffer from low yields, poor product purity, long crystallization times and are difficult if not impractical to scale up.
C. C. Chao in U.S. Pat. No. 4,964,889 (1990) entitled xe2x80x9cSelective adsorption on magnesium containing clinoptilitesxe2x80x9d, in which gases having molecular dimensions equal to or smaller than nitrogen are selectively adsorbed and separated from other gases having molecular dimensions higher than nitrogen. The main drawback is the particle size of the commercial clinoptilolite varies and the particle size of the clinoptilolite will affect the speed and completeness of the ion exchange reaction.
G. Reiss in U.S. Pat. No. 5,114,440 (1992) entitled xe2x80x9cProcess for the adsorptive-oxygen enrichment of air with mixture of calcium zeolite A molecular sieve by means of vacuum swing adsorptionxe2x80x9d, which gives a process for oxygen enrichment of air by means of vacuum swing adsorption using CaA molecular sieve. The drawbacks of this adsorbent are low nitrogen adsorption capacity, low selectivity of nitrogen over oxygen, its preparation needs multistage calcium exchange and its activation process requires very slow heating to prevent hydroxylation.
C. G. Coe et al in U.S. Pat. No. 5,152,813 (1992) entitled xe2x80x9cNitrogen adsorption with a Ca and/or Sr exchanged lithium X zeolitexe2x80x9d, which is directed to a process for separating nitrogen from gas mixtures containing oxygen, hydrogen, argon or helium by use of an at least binary exchanged X-zeolite having lithium and calcium and/or strontium ions in ratio of preferably 5% to 50% calcium and/or strontium and 50% to 95% lithium. The main drawbacks are the preparation of the adsorbent requires multistage cation exchange, its activation process requires very slow heating to prevent hydroxylation and adsorbent is highly sensitive to moisture.
C. C. Chao et al.in U.S. Pat. No. 5,174,979 (1992) entitled xe2x80x9cMixed ion exchanged zeolites and processes for the use thereof in gas separationsxe2x80x9d, wherein lithium/alkaline earth metal X zeolites in which the lithium:alkaline earth metal equivalent ratio is from 95:5 to about 50:50 and lithium/alkaline earth metal A zeolites in which the lithium: alkaline earth metal equivalent ratio is from 10:90 to about 70:30 are found useful for the separation of oxygen and nitrogen from a gas mixture. The main drawbacks are the preparation of the adsorbent requires multistage cation exchange, nitrogen selectivity is only 2-7 and the adsorbent is highly moisture sensitive.
T. R. Gafney et al. in U.S. Pat. No. 5,266,102 (1993) entitled xe2x80x9cOxygen VSA process with low oxygen capacity adsorbentsxe2x80x9d, wherein adsorbents with moderate nitrogen capacity and a high selectivity is used for the separation by VSA process. The main drawbacks are the maximum attainable oxygen purity is only 95% and adsorbent with low nitrogen capacity was used for the separation process.
C. C. Chao in U.S. Pat. No. 5,454,857 (1995) entitled xe2x80x9cAir separation processxe2x80x9d, wherein 60 to 89 equivalent percent calcium exchanged forms of zeolite X having silica/alumina ratio in the range of 2.0 to 2.4 is used in a temperature range of 50xc2x0 C. to xe2x88x9220xc2x0 C. and pressure range of 0.05 to 5 atmospheres. The main drawbacks are the preparation of the adsorbent requires multistage cation exchange and its activation process requirs very slow heating to prevent hydroxylation.
F. R. Fitch et al in U.S. Pat. No. 5,464,467 (995) entitled xe2x80x9cAdsorptive separation of nitrogen from other gasesxe2x80x9d, where in type X zeolites whose charge compensating cations are composed of 95 to 50% lithium ions, 4 to 50% of one or more of aluminum, cerium, lanthanum and mixed lanthanides and 0 to 15% of other ions were used for selectively adsorb nitrogen from gas mixture. The main drawbacks of this adsorbent are its high affinity towards moisture and its preparation requires multistage cation exchange from 5 to 10 fold lithium chloride solutions.
C. C. Chao et al. in U.S. Pat. No. 5,698,013 (1997) entitled xe2x80x9cNitrogen selective zeolitic adsorbent for use in air separation processxe2x80x9d, wherein using 60 to 89 equivalent percent calcium exchanged forms of zeolite X having SiO2/Al2O3 ratio with in the range of 2.0 to 2.4, as selective adsorption for nitrogen in air separation process by pressure swing adsorption. The main drawbacks of this adsorbent are its high affinity towards moisture and its preparation requires multistage calcium exchange and its activation process requirs very slow heating to prevent hydroxylation.
T. C. Golden et al. in U.S. Pat. No. 5,779,767 (1998) entitled xe2x80x9cUse of zeolites and alumna in adsorption processesxe2x80x9d, wherein describes a process for the purification of air by adsorption. The main drawback is this adsorbent is useful only for the adsorption of carbon dioxide, water, hydrocarbons and nitrogen oxides from the gas mixtures.
N. Ogawa et al. in U.S. Pat. No. 5,868,818 (1999) entitled xe2x80x9cAdsorbents for air separation, production method thereof, and air-separation method using itxe2x80x9d, describes the use of crystalline zeolite X having an SiO2/Al2O3 molar ratio of not larger than 3.0, which contains at least 90 mol% lithium cations were used for the air separation by pressure swing adsorption. The main drawbacks of this adsorbent are its preparation requires multistage cation exchange and it is highly sensitive to small amount of moisture.
J. T. Mullhaupt et al. in U.S. Pat. No. 5,945,079 (1999) entitled xe2x80x9cOxygen selective sorbentsxe2x80x9d, describes an invention comprises a process for air separation using oxygen selective sorbent with enhanced selectivity, loading capacities and oxygen uptake rates have a transition metal complex in solid form supported on a high surface area substrate. The drawbacks of this adsorbent are (a) The adsorption is not physical adsorption and hence it is not completely reversible, (b) The preparation and handling of the adsorbent is very difficult and (c) the use of this adsorbent is not commercially economical.
N. V. Choudray et al in No. U.S. Pat. No. 6,030,916 (2000) entitled xe2x80x9cProcess for the preparation of a molecular sieve adsorbent for selectively adsorbing nitrogen from a gaseous mixturexe2x80x9d, describes the preparation of molecular sieve adsorbents containing yttrium and alkali and/or alkaline earth metals as the extra framework exchangeable cations, useful for the separation of oxygen and/or nitrogen from air. The main drawback is the yttrium exchange process requires several cycles to obtain the adsorbent having high nitrogen selectivity.
N. V. Choudray et al in U.S. Pat. No. 6,087,289 (2000) entitled xe2x80x9cProcess for the preparation of a molecular sieve adsorbent for selectively adsorbing oxygen from a gas mixturexe2x80x9d, describes a process for the, preparation of a zeolte based adsorbent containing cerium cations are used for the selective adsorption of oxygen from a gas mixture. The main drawbacks of this adsorbent are its low oxygen capacity (around 3 cc/g at 30xc2x0 C. and 1 atm) and the oxygen selectivity is only in the low-pressure region.
M. Bulow et al. in U.S. Pat. No. 6,143,057 (2000) entitled xe2x80x9cAdsorbents and adsorptive separation processxe2x80x9d, describes the use of an adsorbent composites composed of microparticulate zeolites at least 90% of whose particles have a characteristic particle dimension not greater than about 0.6 microns and a macropore inert binder used for separating nitrogen or carbon dioxide from air. A mixture of type A zeolite, alpha zeolite, type X zeolite and type Y zeolite in which the available cation sites are occupied by a mixture of cations was used as the adsorbent for the selective adsorption. The main drawbacks of this adsorbent are its preparation involves several cycles of cation exchange process and the adsorbent is highly sensitive to moisture.
R. Jain et al. in U.S. Pat. No. 6,231,644 (2001) entitled xe2x80x9cAir separation using monolith adsorbent bedxe2x80x9d, describes the use of monolith bed for separating a first gaseous component from a gas mixture comprising the first gaseous component and a second gaseous component comprising passing the gaseous mixture into an adsorption zone. The main drawbacks of this adsorbent are its high affinity towards moisture and its preparation requires multistage ion exchange process.
N. V. Choudary et al. in Indian patent No. 181823 (1995) entitled xe2x80x9cA process for the preparation of a molecular sieve adsorbent useful in the oxygen enrichment of airxe2x80x9d, describes the use of a zeolite A based adsorbent containing clay binders were used to produce 85-95% pure oxygen by pressure swing adsorption. The main drawbacks of this adsorbent are the low nitrogen selectivity over oxygen (3-5 at 30xc2x0 C. and 1 atm), low nitrogen capacity (around 15 cc/g at 30xc2x0 C. and 1 atm), its high affinity towards moisture and its preparation requires multistage calcium exchange process.
The main object of the present invention is to provide a process for the preparation of a molecular sieve adsorbent for selectively adsorbing nitrogen and argon from a gaseous mixture with oxygen, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a nitrogen selective adsorbent based on synthetic zeolite.
Yet another object of the present invention is to provide argon selective adsorbent (compared to oxygen) based on synthetic zeolite.
Still another object of the present invention is to provide an adsorbent that can visibly refer the decay in adsorption capacity and selectivity due to moisture by its colour change.
Further object of the present invention is to provide an adsorbent with increased adsorption selectivity and capacity for nitrogen from its mixture with oxygen and/or argon.
Still another object of the present invention is to provide an adsorbent, which is selective to nitrogen and argon over oxygen and can be used commercially for the separation of air.
Yet another object of the present invention is to provide an adsorbent, which can be prepared by a single stage cation exchange process.
Accordingly, the present invention provides a xe2x80x9cProcess for the preparation of a molecular sieve adsorbent for selectively adsorbing nitrogen and argon from a gaseous mixture with oxygenxe2x80x9d, which comprises of a molecular sieve adsorbent represented by the general formula,
(Ag2O)x.(M2/nO)y.(Al2O3)6.(SiO2)12.wH2O
where the values of x varies from 4.8 to 6.0, y from 0.0 to 1.2, w being the number of moles of water and M is any metal ion having valancy n.
Accordingly, the present invention provides a single stage process for the preparation of crystalline molecular sieve adsorbent by silver ion exchange, used for selectively adsorbing nitrogen and argon from a gaseous mixture containing oxygen, said process comprising the steps of:
(a) mixing Zeolite A with an aqueous solution of silver salt;
(b) refluxing the solution at 30-90xc2x0 C. for 4-8 hours in dark to obtain a residue;
(c) filtering and washing the residue with water till the residue is free from silver ions; and
(d) drying below 85xc2x0 C. in air followed by under reduced pressure to obtain the crystalline molecular sieve adsorbent having a chemical composition (Ag2O)x.(M2/nO)y.(Al2O3)6.(SiO2)12.wH2O
An embodiment of the present invention, wherein steps (b)-(d) can be optionally performed in the following steps:
(a) mixing Zeolite A with equal amount of silver salt solution;.
(b) heating the mixture at a temperature in the range of 500-575xc2x0 C. in an inert atmosphere;
(c) washing the residue with water till the residue is free from silver ions; and
(d) drying the mixture at an ambient temperature under reduced pressure to obtain the crystalline molecular sieve adsorbent.
Yet another embodiment of the present invention, wherein the value of x varies from 1.2 to 6.0 moles.
Still another embodiment of the present invention, wherein the values of y varies from 0.0 to 4.8moles.
Yet another embodiment of the present invention, wherein w is number of moles of water.
Still another embodiment of the present invention, wherein M is a cation selected from the group consisting of sodium, calcium, potassium or lithium and most preferably sodium.
Still another embodiment of the present invention, wherein the zeolite selected is in the form of granule, powder and pellets.
Yet another embodiment of the present invention, wherein the aqueous solution of silver salt solution is selected from silver per chlorate (AgClO4), silver acetate or silver nitrate (AgNO3).
Further embodiment of the present invention, wherein the concentration of silver salt solution is in the range of 0.25%-15% by weight/volume of zeolite A.
Still another embodiment of the present invention, wherein the ratio of aqueous solution of silver salt with zeolite A is 1:80.
Yet another embodiment of the present invention, wherein said molecular sieve having a high nitrogen adsorption capacity upto 22.3 cc/g at 30xc2x0 C. and 765 mm Hg.
Further embodiment of the present invention, wherein said molecular sieve having selectivity for nitrogen over oxygen is 5-14.6 at 30xc2x0 C.;
Yet another embodiment of the present invention, wherein said molecular sieve having argon adsorption capacity upto 6.5 cc/g at 30xc2x0 C. and 765 mm Hg.
Further embodiment of the present invention, wherein said molecular sieve having selectivity for argon in the range of 1.2-2.0 at 30xc2x0 C.
Yet another embodiment of the present invention, wherein said molecular sieve having a low hydroxylation thereby preventing the necessity of slow heating.
Further embodiment of the present invention, wherein said molecular sieve having a high purification capacity of oxygen greater than 96%.
Yet another embodiment of the present invention, wherein 10 to 100 equivalent percentages of silver ions is loaded into zeolite in a single step using any water soluble silver salt selected from silver nitrate silver perchlorate or silver acetate.
Still another embodiment of the present invention, wherein the zeolite is. ion exchanged with 80 to 100 equivalent percent silver ions and activated molecular sieve adsorbent is orange red/brick red coloured.
Yet another embodiment of the present invention, wherein the molecular sieve adsorbent is dried at a temperature below 85xc2x0 C. preferably at a temperature in the range of 20xc2x0 C. to 80xc2x0 C. in air or under vacuum.
The invention is further explained in the form of the following embodiments:
Zeolites, which are microporous crystalline alumna-silicates, are finding increased applications as adsorbents for. separating mixtures of closely related compounds. Zeolites have a three dimensional network of basic structural units consisting SiO4 and AlO4 tetrahedrons linked to each other by sharing apical oxygen atoms. Silicon and aluminum atoms lie in the center of the tetrahedral. The resulting alumino-silicate structure, which is generally highly porous, possesses three-dimensional pores the access to which is through molecular sized windows. In a hydrated form, the preferred zeolites are generally represented by the following formula,
M2/nO Al2O3.xSiO2.wH2O
where M is a cation, which balances the electrovalence of the tetrahedral and is generally referred to as extra framework exchangeable cation, n represents the valancy of the cation and x and w represents the moles of SiO2 and water respectively. The cation may be any one of the numbers of cations, which will hereinafter be described in detail.
The attributes which makes the zeolites attractive for separation include, an unusually high thermal and hydrothermal stability, uniform pore structure, easy pore aperture modification and substantial adsorption capacity even at low adsorbate pressures. Furthermore, zeolites can be produced synthetically under relatively moderate hydrothermal conditions.
X-ray powder diffraction data was collected using PHILIPS X""pert MPD system equipped with XRK 900 reaction chamber. Comparing the X-ray diffraction data with literature X-ray data checked the crystallinity of the adsorbent particles. The X-ray diffraction at xe2x80x9cdxe2x80x9d values 12.1925, 5.489, 4.086, 3.2818, 2.9773 and 2.7215 were used for comparison.
The zeolite NaA powder [Na12(AlO2)12.(SiO2)12.wH2O] was used as the starting material. X-ray diffraction data showed that the starting material was highly crystalline. The zeolite NaA was mixed with a specified concentration of aqueous silver salt solutions in the ratio 1:80 and treated at 30-90xc2x0 C. for 4-8 hours in the dark. The residue was filtered, washed with hot distilled water, until the washings were free from silver ions (tested with sodium chloride solution) and dried at room temperature to 80xc2x0 C. in air and also under vacuum conditions as specified in the examples. The silver exchange completes in a single step since the equilibrium of the cation exchange reaction favors the easy formation of the product. The extent of silver exchange was determined by Atomic Absorption Spectroscopy.
Oxygen, nitrogen and argon adsorption at 15xc2x0 C. and 30xc2x0 C. was measured using a static volumetric system (Micromeritics ASAP 2010), after activating the sample at 350xc2x0 C. to 450xc2x0 C. under vacuum for 4 hours as described in the Examples. Addition of the adsorbate gas was made at volumes required to achieve a targeted set of pressures ranging from 0.5 to 850 mmHg. A minimum equilibrium interval of 5 seconds with a relative target tolerance of 5.0% of the targeted pressure and an absolute target tolerance of 5.000 mmHg were used to determine equilibrium for each measurement point. The adsorption and desorption are completely reversible, hence it is possible to remove the adsorbed gases by simple evacuation.
The heat of adsorption was calculated using the following equation
Heat of adsorption, xcex94adH0=R{[∂ ln p]/[∂(1/T)]}xcex8
where R is the universal gas constant, xcex8 is the amount of gas adsorbed at a pressure p and temperature T. A plot of Inp against 1/T should be a straight line of slope xcex94adH0/R.
The selectivity of two gases A and B is given by the equation,
xcex94A/B=[VA/VB]P,T
where VA and VB are the volumes of gas A and B adsorbed at any given pressure P and temperature T.
The important inventive steps involved in the present invention are that the molecular sieve adsorbent obtained, (i) is prepared by a single stage ion exchange process using aqueous solution of any silver salt in a temperature range of room temperature to 90xc2x0 C., (ii) is stable during the activation process, hydroxylation chance is very low and hence the activation process does not requre very slow heating, (iii) has a brick red/orange red colour afer the activation, which changes with decay of the adsorption capacity and selectivity due to the presence of moisture in the feed gas mixture, (iv) has, adsorption capacity and selectivity for nitorgen is maximum reported for any zeolite A based adsorbent so far and (v) has argon selectivity over oxygen, which will be useful for the production of oxygen with purity higher than 96%.